The present invention relates to a diversity antenna arrangement according to the species of the main claim.
A diversity antenna arrangement is known from European Patent 02 01 977 A2 for the mobile reception of frequency-modulated vibrations using a receiver, at least two antennas, and a diversity processor, to which an IF (intermediate frequency) signal is fed from the receiver. The diversity processor checks the supplied IF signal and switches over to a different antenna or a different linear combination of antenna signals if the IF signal has interference. Interference is detected if an amplitude break exceeds an amplitude threshold and simultaneously the frequency swing exceeds a frequency swing threshold. An advantage of this method is that, in addition to the circuit arrangement for detecting interference, only an antenna changeover switch is needed. This method can therefore be economically realized in devices, especially if the circuit arrangement for detecting interference is located in a car radio, where the IF amplifier or the demodulator makes available the signals to be evaluated.
Nevertheless, the switchover operation to a different antenna or a different linear combination of antenna signals, especially when weak radio signals are being received, is audible in the loudspeaker. As a result, the diversity antenna arrangement adds further interference to reception signals that already have interference. When the switching is more frequent, the interference is more pronounced.
From German Patent 36 34 439 A1, a method and a circuit arrangement for receiving radio waves are known. In this context, a diversity method is described in which the signal received from each antenna is converted in the receiver to the intermediate frequency IF. The IF signals of the individual antennas are weighted using coefficients, and the weighted signals are added to yield a composite signal. The coefficients are generated in the sense of minimizing the temporal amplitude fluctuations of the IF composite signal.
In this method, it is advantageous that no switching is performed and therefore no switching noises are audible. For this purpose, for each antenna, in addition to the circuit arrangement for regulating the coefficients, a complete radio input part is required, having a pre-stage, a mixer, and an IF filter.